Syntax

#include <stdlib.h>
onexit_t _onexit(onexit_t func);

• onexit records the address of a function func to call when the program ends normally. Successive calls to _onexit create a stack of functions that run in a last-in-first-out order. The functions passed to _onexit cannot take parameters.

  You can record up to 32 termination functions with calls to _onexit and atexit. If you exceed 32 functions, _onexit returns the value NULL.

  Note: For portability, use the ANSI/ISO standard atexit function, which is equivalent to _onexit.

If successful, _onexit returns a pointer to the function; otherwise, it returns a NULL value.

This example specifies and defines four distinct functions that run consecutively at the completion of main.

#include <stdio.h>
#include <stdlib.h>

int fn1(void)
{
   printf("next.\n");
}

int fn2(void)
{
   printf("run ");
}

int fn3(void)
{
   printf("is ");
}

int fn4(void)
{
   printf("This ");
}

int main(void)
{
   _onexit(fn1);
   _onexit(fn2);
   _onexit(fn3);
   _onexit(fn4);
   printf("This is run first.\n");
   return 0;

   /****************************************************************************
      The output should be:

      This is run first.
      This is run next.
   ****************************************************************************/
}

• abort
  
• atexit
  
• exit
  
• exit

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